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Old 06-30-2020, 11:57 AM   #8501
su_ba_roooo
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Quote:
Originally Posted by Norm Peterson View Post
You have to look at more than just 'XL' and 'SL'. Basically, what you need to be doing is matching the rated load of your OE tires at their recommended inflation pressures. For the 2015-up WRX, I think the OE tires are 245/40-18, 97 in XL, and the inflation pressures are 33/32 psi.

After that it gets a little more complicated. The 255/40-18 is a 95 in SL, which actually corresponds to a 99 in XL (larger than OE). The 255/35 is a 94 in XL and is a slightly smaller tire than OE in terms of load capacity. In either case, you'd want to set inflation pressures slightly different from Subaru's 33/32. You could actually drop about 2 psi off of the door sticker number for the 255/40's, but you'd have to add about 4 psi for the 255/35's. Three load index numbers worth of correction is as far as I'm normally willing to consider.

Reinforcement is more for the XL tires being rated to 42 psi vs the SL tires to only 36 psi. I suspect any handling benefit would be mostly incidental.


Norm
Thanks Norm. Sounds like either option works fine. The 255/40 would fill the wheel well a little more and should be more forgiving of potholes and such, especially at 30/31 psi. compared to the 255/35 at 38/39 psi. . But maybe it's all semantics in day to day driving.

*edited. Tire Rack suddenly dropped the price of the 255/40R18 to $135/ea shipped so had to jump on that.
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Last edited by su_ba_roooo; 07-05-2020 at 11:13 PM.
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Old 07-27-2020, 01:25 PM   #8502
SilverBeast15
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Quote:
Originally Posted by DrDanimalSize View Post
also in for what tire size
Apparently you donít need any fender roll or coil drop etc... for a 255/35/18.

A 40 section sidewall would be too tall.
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Old 07-27-2020, 05:16 PM   #8503
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Originally Posted by Scino View Post
I want Kojin 18x9.5 et30, but I think I will go with Raijin 18x9.5 et35 to avoid more work. I'm new the low offset thing, can anyone tell me what should be done on both set ups? I just want to drop it on lowering springs, something like RCE black.
For 18x9.5 +38 a company told me 255/35r18 tires will have clearance.
But when I check specs for rims sizes it shows me for this particular rims size 285/35r18
So I am also confused... how can I put a smaller width tire on a wider rim? Because there is a difference between 255 and 285.

Anyone know if that company is correct?
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Old 07-27-2020, 05:17 PM   #8504
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Originally Posted by Scino View Post
I want Kojin 18x9.5 et30, but I think I will go with Raijin 18x9.5 et35 to avoid more work. I'm new the low offset thing, can anyone tell me what should be done on both set ups? I just want to drop it on lowering springs, something like RCE black.
For 18x9.5 +38 a legit company told me 255/35r18 tires will have clearance without anything needed to be done to fenders or coils etc.
But when I check specs for rims sizes it shows me for this particular rims size 285/35r18.

So I am also confused... how can I put a smaller width tire on a wider rim? Because there is a difference between 255 and 285.

Anyone know if that company is correct?
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Old 07-27-2020, 06:42 PM   #8505
dpetro1
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Quote:
Originally Posted by SilverBeast15 View Post
For 18x9.5 +38 a legit company told me 255/35r18 tires will have clearance without anything needed to be done to fenders or coils etc.

But when I check specs for rims sizes it shows me for this particular rims size 285/35r18.



So I am also confused... how can I put a smaller width tire on a wider rim? Because there is a difference between 255 and 285.



Anyone know if that company is correct?
Tires have a range of wheel widths they are approved for. Generally, 255/35/18 is ok on a 9.5" wheel.
That said, it is technically undersized versus stock.
I personally would use 265/35 which is closer to stock size.
Clearance and rubbing depends on a lot of factors including how low you are, camber specs, spring rates, etc.
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Old 07-28-2020, 07:41 AM   #8506
Norm Peterson
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Quote:
Originally Posted by SilverBeast15 View Post
For 18x9.5 +38 a company told me 255/35r18 tires will have clearance.
But when I check specs for rims sizes it shows me for this particular rims size 285/35r18
So I am also confused... how can I put a smaller width tire on a wider rim? Because there is a difference between 255 and 285.
Tires can be mounted on any rim width that falls within tire industry guidelines.

The tire industry range of rim widths for the 255/35-18 size runs from 8.5" all the way out to 10", inclusive.

The tire industry range of rim widths for the 285/35-18 size runs from 9.5" to 11".


Quote:
Anyone know if that company is correct?
So yeah, they're correct as far as either size being legitimately mounted on 9.5" wide wheels goes. Why they're recommending the 285 when 9.5" is barely wide enough for it is not at all clear, but it's probably catering to people wanting to have some sort of bragging rights ("my car has 285's on it").


dpetro is correct in that 255/35-18 is undersize, at least if your car's original size is 245/40-18. You could crutch that by running 255/35-18's at something like 36 psi, but count on tread center wear and ride quality both suffering as a result. All else equal, better to just go with 265/35-18's and door-sticker inflation pressures.


Honestly, 9.5" wheels with +45 offset would likely make for an easier fit. You want an inch more rim width, and +35 wastes 10mm that could be better used for fender-side clearance without getting any closer to the struts and other inside stuff than the OE wheels and tires do.


Norm
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Old 07-30-2020, 03:07 AM   #8507
EBeland17
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I know this might seem redundant, but i just want some advice before i make my final decision. I am currently running my 2017 wrx on the stock Dunlops 245/40/18 on a set of 18x9.5+35 wheels. The car is on coilovers with roughly -1.2" -1.0" drop (front/rear). The fitment looks great but the wheels got warped and bent from the nasty roads in the local area (and the stretched tires).
I have a new set of wheels arriving in a month with similar dimensions but slightly less poke (18x9.5+40) and was thinking of getting Michelin pilot sport 4S summer tires but I'm not sure of the size yet. Either 255/40 or 265/35 but I don't want to modify the fenders. I may also raise the ride height just a bit too. Any input is appreciated.
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Old 07-31-2020, 03:16 PM   #8508
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Originally Posted by EBeland17 View Post
I know this might seem redundant, but i just want some advice before i make my final decision. I am currently running my 2017 wrx on the stock Dunlops 245/40/18 on a set of 18x9.5+35 wheels. The car is on coilovers with roughly -1.2" -1.0" drop (front/rear). The fitment looks great but the wheels got warped and bent from the nasty roads in the local area (and the stretched tires).
I have a new set of wheels arriving in a month with similar dimensions but slightly less poke (18x9.5+40) and was thinking of getting Michelin pilot sport 4S summer tires but I'm not sure of the size yet. Either 255/40 or 265/35 but I don't want to modify the fenders. I may also raise the ride height just a bit too. Any input is appreciated.
All of the following tire sizes I've listed below can technically be used on 9.5" wheels, however, the one's in bold are the most popular. Drivers are motivated by different things, so an analysis really needs to be done depending on what it is that you are trying to accomplish. Keep in mind that not all tires are created equal in terms of width and sidewall construction/shape.

For a street car running PS4S with minimal camber, you can automatically remove the 275's and 285's off the list as those are really only warranted on track/race cars. Since you want to go wider than your current 245's to gain more rim protection and avoid any form of stretch, you can also remove 245's.

Deciding between 255/35-18, 255/40-18 and 265/35-18 really comes down to whether or not each of these sizes is available in the compound you're choosing to run (they are all available in the PS4S), and how you want to prioritize grip (width), comfort (sidewall) and fitment (whether or not you're willing to perform any additional modifications to avoid rubbing under suspension compression).

The 255/35-18 is the easiest to fit of the three as they are not quite as wide as the 265's, and they are not quite as tall as the 255/40's. No modifications would typically be necessary.

265/35-18 arguably suits the 9.5" wheel width the best in that it leverages the width of the wheel and better protects the inner and outer lips of the wheels from damage. Depending on factors like ride height, camber settings and even spring rates, you may lightly rub under suspension compression. If you have some negative camber dialed in, you typically will not have any issues.

If you want a little more sidewall, 255/40-18 would be the best choice. If you experience any rubbing under suspension compression it wouldn't be because of the width, rather it would be due to the slight increase in height over stock.

There is no wrong answer here.

245/40-18 - 25.7" (stock)
255/35-18 - 25" (-2.7% shorter)
255/40-18 - 26" (1.2" taller)
265/35-18 - 25.3" (-1.6% shorter)
275/35-18 - 25.6" (-0.4% shorter)
285/30-18 - 24.7" (-3.9% shorter)

Here are some supportive photos of each of these tire sizes, all mounted on our EC-7 18x9.5" ET38 WRX/STI wheels (2mm more aggressive than the wheels you went with). At the end of the day ride height, tire model and camber settings will all change the final outcome from one car to another, even if the same tire size and wheel specs are used.

245/40-28 Michelin PS4S


255/35-18 Federal


255/40-18 Conti ExtremeContact Sport


265/35-18 Nankang AR-1


275/35-18 Toyo RR




- Ryan

Last edited by APEXRaceParts; 07-31-2020 at 03:30 PM.
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Old 07-31-2020, 03:41 PM   #8509
fullah
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Droool 275/35.
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Old 08-01-2020, 07:42 AM   #8510
Norm Peterson
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'08 Mustang GT (the toy)

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One thing about the 255/35-18 size - it's something like three load index numbers smaller of a tire than the OE 245/40-18. You'd need to inflate it to 3 or 4 psi more than the 245/40 in order to maintain the same rated load capacity.

Seems to me, that would make the 255/35-18 the least attractive of the above three sizes shown in boldface.


Norm
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Old Yesterday, 11:41 PM   #8511
EBeland17
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Quote:
Originally Posted by APEXRaceParts View Post


All of the following tire sizes I've listed below can technically be used on 9.5" wheels, however, the one's in bold are the most popular. Drivers are motivated by different things, so an analysis really needs to be done depending on what it is that you are trying to accomplish. Keep in mind that not all tires are created equal in terms of width and sidewall construction/shape.

For a street car running PS4S with minimal camber, you can automatically remove the 275's and 285's off the list as those are really only warranted on track/race cars. Since you want to go wider than your current 245's to gain more rim protection and avoid any form of stretch, you can also remove 245's.

Deciding between 255/35-18, 255/40-18 and 265/35-18 really comes down to whether or not each of these sizes is available in the compound you're choosing to run (they are all available in the PS4S), and how you want to prioritize grip (width), comfort (sidewall) and fitment (whether or not you're willing to perform any additional modifications to avoid rubbing under suspension compression).

The 255/35-18 is the easiest to fit of the three as they are not quite as wide as the 265's, and they are not quite as tall as the 255/40's. No modifications would typically be necessary.

265/35-18 arguably suits the 9.5" wheel width the best in that it leverages the width of the wheel and better protects the inner and outer lips of the wheels from damage. Depending on factors like ride height, camber settings and even spring rates, you may lightly rub under suspension compression. If you have some negative camber dialed in, you typically will not have any issues.

If you want a little more sidewall, 255/40-18 would be the best choice. If you experience any rubbing under suspension compression it wouldn't be because of the width, rather it would be due to the slight increase in height over stock.

There is no wrong answer here.

245/40-18 - 25.7" (stock)
255/35-18 - 25" (-2.7% shorter)
255/40-18 - 26" (1.2" taller)
265/35-18 - 25.3" (-1.6% shorter)
275/35-18 - 25.6" (-0.4% shorter)
285/30-18 - 24.7" (-3.9% shorter)

Here are some supportive photos of each of these tire sizes, all mounted on our EC-7 18x9.5" ET38 WRX/STI wheels (2mm more aggressive than the wheels you went with). At the end of the day ride height, tire model and camber settings will all change the final outcome from one car to another, even if the same tire size and wheel specs are used.

245/40-28 Michelin PS4S


255/35-18 Federal


255/40-18 Conti ExtremeContact Sport


265/35-18 Nankang AR-1


275/35-18 Toyo RR




- Ryan
Your reply is very much appreciated, the pictures and input helped a lot. The 255/35 is definitely not an option based on what Norm said and the fact of them being so short. The 255/40 looks better than I expected, if i choose that i will probably raise the car about 1/4 inch to prevent the tall tires rubbing and just for extra clearance overall. The 265/35 is ultimately what i want for grip and better protection, if i go with that i will have to adjust the front camber as it is currently -1, rear is -3 so that may not need to be changed. I will look at overall tire width on the PS4S as compared to other options for 265.
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